One of the most important aspects in presenting a multimedia stream composed of a video and audio stream is the perception of synchronization between displayed video frames and corresponding audio information. A lag of more than one-quarter to one-half of a second between the audio and video information generally leads to perception problems by trained observers. Any lag beyond one-quarter to one-half of a second becomes distracting to ordinary observers. Typically, the maintenance of synchronization between audio and video forms the cornerstone of any multimedia decoder.
Conventional approaches include many different mechanisms for maintaining audio-video synchronization during a multimedia presentation. One common approach is to periodically embed the values of a reference clock in the stream, or to provide snapshots of such a clock for the corresponding audio and video streams. The ability to recover the master clock during the decode phase will help ensure the correct overall rate of presentation. Embedded time-stamps for audio and video streams also help ensure proper synchronization during playback between the audio and video streams.
In recent years, there has been a rise in popularity of an entirely different class of multimedia streams. Such multimedia streams are void of embedded timestamps. These multimedia streams primarily rely on consistent interleaving of the audio and video data for synchronization. Such streams are created on a personal computer, which avoids the need for any central-clock recovery mechanism. In addition, an inherent assumption at the distribution of a perfect stream with perfect synchronization between the audio and video streams avoids the need for any embedded time-stamps while relying on the physical relationship of the audio and video packets. The popularity of these streams has lead to expanding such implementations into the consumer electronic world. However, the consumer electronic world demands perfection in synchronization for signals without embedded time-stamps is now a challenge.
It would be desirable to provide a method and/or apparatus for maintaining audio-video synchronization during the playback of multi-media streams that do not contain embedded time-stamps.